Method for operating a hydraulic pump arrangement, and hydraulic pump arrangement

ABSTRACT

A hydraulic pump arrangement of a portable hydraulic tool operates by an autonomous power supply or is releasably connected to the hydraulic tool by a hose and driven by an electrical power source. A load-dependent control of the hydraulic pump switches between a loaded state and a non-loaded state. A higher electrical power supply is implemented for the loaded state and a lower electrical power supply is implemented for the non-loaded state. To provide energy savings and problem-free operation even in different system pressure conditions, a method fixes a control variable for the load-dependent control that is dependent on work being performed by the hydraulic pump motor. A first threshold value at which switching from the non-loaded state to the loaded state takes place and a second threshold value at which switching from the loaded state to the non-loaded state takes place are assigned to the control variable.

The present invention relates to a method for operating a hydraulic pump arrangement in accordance with the preamble of claim 1 and the invention also relates to a hydraulic pump arrangement in accordance with the preamble of claim 9.

TECHNICAL FIELD

Hydraulic pump arrangements of the type described above are used for a variety of applications. They are generally portable and are therefore equipped with an autonomous power supply for example a battery or the like. On the one hand, they are used as a component of hydraulically driven rescue tools such as so-called spreading or cutting tools that are used by emergency services for rescuing people who are trapped or buried in wrecks of vehicles. On the other hand, they are also used in tool technology, for example to reduce the size of pieces of scrap etc. Generally, the switching valves for operating the hydraulically driven tools are located directly on the tool so that the operator can directly control the tool as required by way of the switching valves. The hydraulic pump arrangements that are necessary for the drive are therefore generally connected to the individual tools by way of flexible hydraulic hoses. Hydraulic hoses can have a variety of lengths depending upon individual applications and this leads to a variety of pressure ratios. In addition, there are a variety of different rescue tools for different individual applications and said different rescue tools are to be changed where necessary on site if the situation demands it. Different rescue tools in turn lead to different power levels, for example different motor idle pressures. In order to extend the service life of the tools, every effort is made to extend the service life of the power source as much as possible. In the past, a system of providing energy saving modes was adopted. An energy saving mode of this type is achieved by way of example by means of switching from a loaded state to a non-loaded state (switching the operating state), if it is not necessary for the tool to perform further work.

PUBLISHED PRIOR ART

A portable hydraulic system in accordance with the preamble of claim 1 is disclosed in U.S. Pat. No. 5,678,982. This hydraulic system already comprises a process of controlling the operation in a loaded state and a non-loaded state accordingly with the aid of a switch that is switched between the loaded state and the non-loaded state in dependence upon a pressure threshold value. This pressure threshold value becomes an absolute pressure and is established by means of a pressure sensor that taps the pressure at the output of the pump and controls a switching unit. The switching unit is actuated in dependence upon the absolute pressure at the output of the pump, said output pressure being established by the pressure sensor, and the system is switched from a non-loaded state to a loaded state or vice versa. This known hydraulic system functions well as long as the components of the system, namely the hydraulic pump arrangement, the hose line and also the tool, match one another. However, replacing tools with different motor idle pressures and/or using different hose lengths leads to malfunctions.

OBJECT OF THE PRESENT INVENTION

The object of the present invention is to provide a new method for operating a hydraulic pump arrangement and also to provide a new hydraulic pump arrangement that on the one hand, ensures that energy is saved and on the other hand, renders possible a problem-free operation even in the case of different system pressure ratios.

ACHIEVING THE OBJECT OF THE INVENTION

The present object is achieved in the case of the method in accordance with the generic type by means of the features of the characteristic part of claim 1 and also in the case of the hydraulic pump arrangement in accordance with the generic type by means of the features of the characteristic part of claim 9.

Expedient embodiments of the method in accordance with the invention and also of the hydraulic pump arrangement in accordance with the invention are described in the dependent claims.

By virtue of the fact that at least one input value is established for control purposes as a control variable S and said control variable is dependent upon the work that is to be performed by the motor of the hydraulic pump arrangement, malfunctions as a result of the changing pressure ratios in the case of varying the hose length, in the case of changing tools, in the case of fluctuating temperatures etc., are effectively eliminated because the relevant control variable is directly dependent upon the work that is to be performed by the motor. The first and also the second threshold value W1 or rather W2 are different. In particular, the first threshold value W1 is lower than the second threshold value W2. The control process renders it possible, even in the case of stopping the movement of the tool while the tool is under load, for example if the emergency doctor requires even further space in order to care for a person who is trapped in a vehicle and it is necessary therefore once again to control the rescue tool (for example a spreader) to change from the loaded state to the non-loaded state and also to subsequently switch from the non-loaded state to the loaded state during a further movement of the tool while the tool is under load.

In particular, it is also possible to establish two control variables S1 and S2, for example the motor current and the pressure, in an expedient manner for the load-dependent control of the hydraulic pump arrangement and said two control variables are dependent as input values on the work that is to be performed by the motor of the hydraulic pump arrangement, wherein a first threshold value W1, at which switching from the non-loaded state to the loaded state takes place, is assigned to the first control variables S1 (motor current), and a second threshold value W2, at which switching from the loaded state to the non-loaded state takes place, is assigned to the control variables S2. As a consequence, in the case of problems defining the signal of one of the control variables, the other control variable is drawn upon as an auxiliary variable and vice versa. This renders possible a precise switching process.

The operation of the hydraulic pump arrangement is suitable for multiple operating situations by virtue of the fact that the second threshold value is preferably a variable value that is continuously updated, in other words a storage medium is overwritten, during operation of the hydraulic pump arrangement.

In accordance with one expedient embodiment of the method in accordance with the invention, a third threshold value W3 is preferably also assigned to the control variable S, wherein switching from the loaded state to the non-loaded state takes place in dependence upon both the second threshold value W2 and also the third threshold value W3. As a consequence, an excessively rapid switch from the loaded state to the non-loaded state is avoided.

In the case of the third threshold value W3, said threshold value is preferably a fixed predefined value of the control variables S.

The motor current is drawn upon in an expedient manner as a control variable S, in other words the current consumption of the motor of the hydraulic pump and said current consumption represents a measurement for the work that is to be performed by the motor of the hydraulic pump arrangement. The process of determining the motor current can be performed in various ways.

Alternatively, it is also possible for this purpose to draw upon the pressure or the motor torque as the control variable S.

In all cases, the values are preferably time related, in other words values that represent the change of the control variables S over a predefined time interval.

In an expedient manner, the hydraulic pump device in accordance with the invention detects the motor current by means of measuring a drop in voltage across a resistor and it is possible to deduce the value of the motor current from said measurement.

Alternatively, it also possible to provide a current measurement device, such as for example an ampere meter or the like, for measuring the current in the motor line.

A rewritable storage medium of the type RAM or EEPROM is expediently used as a storage medium.

In the case of a drop in load, the rotational speed of the motor is reduced by means of changing the motor voltage in its rotational speed. For this purpose, a voltage is applied at the motor as a voltage pulse, preferably having a uniform pulse height, in other words intensity, however having a different pulse width. The voltage is consequently modulated. The current adjusts in response to the external load.

DESCRIPTION OF THE INVENTION WITH REFERENCE TO EXEMPLARY EMBODIMENTS

Expedient embodiments of the invention are further explained hereinunder with reference to figures. In the drawings:

FIG. 1 schematically illustrates a first embodiment of the present invention;

FIG. 2 illustrates a flow diagram of the process of controlling the hydraulic pump arrangement in accordance with the embodiment in accordance with FIG. 1;

FIG. 3 illustrates a diagrammatic illustration of the curve of the motor current of the hydraulic pump arrangement in accordance with FIG. 1;

FIG. 4 illustrates a further diagrammatic illustration of the curve of the motor current of the hydraulic pump arrangement in accordance with FIG. 1 with a break in the operation;

FIG. 5 schematically illustrates a further embodiment of the present invention;

FIG. 6 schematically illustrates the use of the hydraulic pump arrangement in accordance with the invention in the case of different hose lengths, and also

FIG. 7 schematically illustrates the use of the hydraulic pump arrangement in the case of different types of hydraulic tools.

The reference numeral 1 describes in its entirety the hydraulic pump arrangement in accordance with the invention. It is portable and is connected by way of preferably flexible hose lines 15 to an exchangeable hydraulic tool 18. Coupling arrangements 14 and 16 respectively can be provided at the output of the hydraulic pump arrangement 1 and also at the input of the hydraulic tool 18 for a rapid coupling and accordingly decoupling of the hydraulic pump arrangement.

The hydraulic pump arrangement 1 comprises a pump 2 and also an electric motor 4 that drives the pump 2. The electric motor 4 is supplied with electrical power from a battery 19 or rather a power supply network. The pump 2 comprises a tank 3 for the hydraulic fluid. A pressure line leads from the pump 2 and the tank line leads from the tank 3 out of the hydraulic pump arrangement 1 to the respective coupling arrangement 14.

The reference numeral 10 describes a control device for the sequence control of the hydraulic pump arrangement 1. This control device comprises in particular a microcontroller 6, a storage medium 7, a generator 8 for the purpose of pulse width modulation and also an analogue/digital converter 9. The above-mentioned components are attached to a circuit board. The microcontroller 6 is preferably connected to a main switch 5. The electrical circuit from the battery 19 to the microcontroller 6 is either closed or interrupted by means of said main switch. The electric motor 4 can be directly connected to the main switch 5 so that the former is supplied with electrical power from the battery 19 in the case of switching on the main switch 5.

In accordance with the present invention, in particular the motor current, in other words the current that the electric motor 4 consumes during the operation of the hydraulic pump arrangement, is measured as a control variable S for the load switching (switching the operating state). This switching process is performed in the case of the embodiment that is illustrated in FIG. 1 in an expedient manner with the aid of a resistor 13. The resistor 13 is connected via a signal line 23 to the analogue/digital converter 9. The latter converts the analogue signals into digital signals for the purpose of further signal evaluation.

The process of determining the current is preferably performed indirectly by way of the drop in voltage across the resistor 13. This drop in voltage is amplified by means of the amplifier 21 and is provided by way of the signal line 23 as an input into the analogue/digital converter 9. The digital data are processed by the microcontroller 6 and are compared with the data in the storage medium 7 (threshold values from the control logic). As a consequence, the corresponding pulse width is output in the generator 8 for the pulse width modulation and the power transistor 11 (for example a MOSFET) transistor is correspondingly connected. If the power transistor 11 is disconnected, the current flows by way of the free-wheeling diode 12 that is connected in parallel to the motor 4. The minus terminal of the motor 4 is so-to-speak pulsed. Likewise, however, it is also possible that the plus terminal is pulsed.

The abovedescribed embodiment of the present invention has two operating states, namely a loaded operation and also a non-loaded operation. During a loaded operation the electric motor 4 is supplied with the full electrical power (for example 24V), and during a non-loaded operation the electric motor is supplied with a reduced electrical power (for example 2V). The switching process is performed by means of the control unit 10 by means of the generator 8 for the pulse width modulation and said generator cooperates with the power transistor 11 as described above. The generator 8 for the pulse width modulation process together with the power transistor 11 preferably forms continuous, periodic current signals that only differ in their pulse width in dependence upon the respective loaded state. The pulse width during the loaded state is greater in relation to a unit of time and the pulse width during the non-loaded state is smaller.

The respective hydraulic tool 18 comprises a hydraulic cylinder 20 that is connected by way of a switching valve 17 to the hose lines 15. In the case of the switching valve 17, said valve is preferably a so-called 4/3 directional valve with which it is possible to establish the two movement directions (forwards and backwards) of the hydraulic cylinder 20 and also a motor idle position (medium position of the switching valve 17). The switching valve 17 is provided by way of example in the form of a so-called star-grip directly on the tool 18.

The function sequence of the hydraulic pump arrangement 1 in accordance with the invention is further explained hereinunder with reference to FIG. 2. If the hydraulic pump arrangement 1 in accordance with the invention is set in operation by means of switching on the main switch 5, the electric motor 4 is supplied with electrical power (in this case for example with 2V) in the non-loaded region. Simultaneously, in the manner that is described in the introduction, the current that is consumed by the electric motor 4 is continuously determined. In this case, a difference current, in other words a current difference, is determined by way of a fixed defined time interval. A first threshold value W1 is stored in the control device 10. The determined value of the current consumption of the electric motor 4 is compared with the first threshold value W1 in the logic of the microcontroller 6. If the determined value of the current consumption is lower than the first threshold value W1, the hydraulic pump arrangement remains in the non-loaded region. Provided that the determined value of the current consumption is greater than the first threshold value W1, the hydraulic pump arrangement switches into the loaded region. In the loaded region, the electric motor 4 is operated with a voltage of for example 24V.

Directly after switching up into the loaded region, the current is determined and is stored as the threshold value W2 in the storage medium 7. The last value that relates to this is overwritten in the storage medium. An individual threshold value W2 that is dependent upon the actual factors (temperature, connected hose length, type of the rescue tool) is consequently always stored in the storage medium 7 after the process of switching into the loaded region.

Furthermore, a third threshold value W3 that represents a fixed value is provided in the control process. If the continuously measured consumed current of the electric motor 4 remains greater than the second threshold value W2 or third threshold value W3, the control process remains in the loaded state. If the continuously measured current that is consumed by the electric motor 4 is lower than the second threshold value W2 and is also lower than the third threshold value W3, the control process switches to the non-loaded state (2 V).

FIG. 3 illustrates the control process of the motor drive with reference to a current curve I that is plotted over the time axis t. In the case of actuating the main switch 5, the electric motor is at first supplied with a voltage of 2 V. After a specific time interval, the control valve 17 is actuated by the operator at which point the hydraulic cylinder 20 of the tool 18 is moved forwards under no external load. The measured current I exceeds the first threshold value W1 so that the control device 10 converts the operation from 2 V to 24 V. As long as no external load is present on the movement of the tool, the electric motor 4 (after a specific transient response) only requires an essentially constant current. As soon as an external load affects the tool movement, the current that is required by the electric motor 4 considerably increases until a release as a result of the terminated deformation or severing of a relevant item or component or the like. After the control valve 17 has been brought into the neutral position (motor idle), the amount of current that is required by the electric motor 4 considerably decreases. As soon as the current falls below the third threshold value W3 and also below the second threshold value W2, the control process switches to the non-loaded operation (2 V).

The illustration in accordance with FIG. 4 differs from that in accordance with FIG. 3 by virtue of the fact that a break in the operation is implemented during the operation. The break in the operation can occur, as in FIG. 4, for example if the operator becomes unsure, briefly releasing the star-grip, in order then to continue working. In this case, the control valve 17 is brought into the neutral position (motor idle position) by the operator. The amount of current that is required by the electric motor 4 rapidly decreases. If the current consumption has fallen below both the third threshold value W3 and also the second threshold value W2, the control process switches from the loaded operation to the non-loaded state. As soon as the working cycle is re-commenced, the operator actuates the control valve 17 again so that current is once again drawn by the electric motor 4. As a result of the break in the operation, switching takes place from the non-loaded state to the loaded operation, as a consequence of which a new threshold value W2 is established and stored in the storage medium 7. Since the break in the operation takes place in the proximity of the peak of the current curve, a very high threshold value W2 is stored. In order to avoid an immediate switching process, the third threshold value W3 is provided. Only if the determined motor current has also fallen below the third threshold value W3 does the control process switch from the loaded operation to the non-loaded state.

An alternative embodiment of the present invention is disclosed in FIG. 5. In contrast with the embodiment according to FIG. 1, this embodiment of the invention has a current measuring device 22 by way of example in the form of an ampere meter in lieu of an electrical resistor. Said current measuring device measures the current in the motor line. The current measuring device 22 is likewise connected to the analogue/digital converter 9 by way of a signal line 23. In the case of the embodiment according to FIG. 5, two further connectors T and also P are provided.

In addition, during the process of controlling the load, the pressure and/or the temperature can also be drawn upon as an additional control variable, for example the pressure as a leading variable and the current as an auxiliary variable for the purpose of ensuring a precise switching process by means of a higher signal resolution. By virtue of detecting the temperature, it is rendered possible to use an additional deciding criterion in order to evaluate the main variables. These variables are described in FIG. 5 with the input values T (temperature) and also P (pressure) at the analogue/digital converter 9.

As is illustrated in FIG. 6, it is possible to connect the hydraulic pump arrangement 1, depending upon the desired purpose, to the same tool 18 by way of coupling arrangements 14 and 16 respectively and also by way of variable hose lengths 15 a and 15 b respectively. The pressure ratios that are present in the system change as a result of the use of different hose lengths. However, this change in pressure ratios does not lead to malfunctions since the process of controlling the operation of the hydraulic pump arrangement 1 is provided in accordance with the invention by way of the motor current as a control variable S and said variable is directly dependent on the work that is to be performed by the motor of the hydraulic pump arrangement 1.

If the pressure ratios change as a result of a comparably longer hose line 15 then the motor current also changes. However, said motor current is compared with at least in part variable current thresholds (adaptive control process).

The same also applies when exchanging the tools 18 a to 18 c, as is also illustrated in FIG. 7. The operating pressure ratios also change in this case. By way of example, a tool 18 a in the form of a cutter has a different current consumption in the motor idle mode than a spreader (tool 18 b). This difference also applies as a consequence in the process of controlling the hydraulic pump arrangement 1.

The same also applies for a change of the length of the hose lines in the case of a simultaneous change of the type of tool 18 a to 18 c.

Alternatively, the pressure and/or the torque can also be drawn upon as a control variable S, in other words as a control parameter, in lieu of the motor current.

LIST OF REFERENCE NUMERALS

-   1 Hydraulic Pump Arrangement -   2 Pump -   3 Tank -   4 Motor -   5 Main Switch -   6 Microcontroller -   7 Storage Medium -   8 Generator for Pulse Width Modulation -   9 Analogue/Digital Converter -   10 Control Device -   11 Power Transistor -   12 Free-Wheeling Diode -   13 Resistor -   14 Coupling Arrangement -   15 Hose Line -   16 Coupling Arrangement -   17 Switching Valve -   18 Tool -   19 Battery or rather Power Supply Network -   20 Hydraulic Cylinder -   21 Amplifier -   22 Current Measuring Device -   23 Signal Line 

1. A method for operating a hydraulic pump arrangement of a portable hydraulic tool operated by an autonomous power supply, wherein the hydraulic pump arrangement is releasably connected to the hydraulic tool by a hose connection and is driven by an electrical power source and a load-dependent control of the hydraulic pump takes place by switching from a loaded state to a non-loaded state and vice versa, wherein a first higher electrical power supply is implemented for the loaded state and a second lower electrical power supply is implemented for the non-loaded state, the method comprising: establishing at least one control variable for the load-dependent control of the hydraulic pump arrangement and said control variable is dependent as an input value on work that to be performed by a motor of the hydraulic pump arrangement, assigning to the control variables a first threshold value at which switching from the non-loaded state to the loaded state takes place, and where necessary assigning to the control variables a second threshold value at which switching from the loaded state to the non-loaded state takes place.
 2. The method as claimed in claim 1, wherein two control variables and are established for the load-dependent control of the hydraulic pump arrangement and said control variables are dependent as input values on the work to be performed by the motor of the hydraulic pump arrangement, a first threshold value at which switching from the non-loaded state to the loaded state takes place is assigned to the first control variables, and a second threshold value at which switching from the loaded state to the non-loaded state takes place is assigned to the control variables.
 3. The method as claimed in claim 1, wherein after switching on the hydraulic pump arrangement but before the tool moves, the control process maintains the supply of power to the electric motor from the electrical power source at the second, lower electrical power supply level, as the tool begins to move under no external load, the control process switches the supply of power to the motor from the electrical power source to the first, higher electrical power supply level.
 4. The method as claimed in claim 1, wherein as movement of the tool under load is stopped, a process of switching from the loaded state to the non-loaded state takes place and if the movement of the tool is continued, in turn a switching process from the non-loaded state to the loaded state takes place.
 5. The method as claimed in claim 1, wherein the second threshold value is a variable value and is updated during the operation.
 6. The method as claimed in claim 1, wherein a third threshold value is assigned to the control variables and a process of switching from the loaded state to the non-loaded state takes place in dependence upon the second threshold value and the third threshold value.
 7. The method as claimed in claim 1, wherein the control variable is the motor current.
 8. The method as claimed in claim 1, wherein the control variable is the pressure and/or the motor torque.
 9. The method as claimed in claim 1, wherein the control variable is a value related to time.
 10. A hydraulic pump device for driving a portable hydraulic tool comprising: a housing, a hydraulic pump, an electric motor for the purpose of driving the hydraulic pump, a coupling device for the purpose of connecting the hydraulic pump device to flexible connecting lines for supplying the hydraulic tool with hydraulic fluid, a control device for the load-dependent control of rotational speed of the motor; means for detecting at least one of the control variables and said control variable is dependent as an input value upon work to be performed by the motor of the hydraulic pump arrangement, means for comparing the detected control variables with a first threshold value, where necessary means for comparing the detected control variables with a second threshold value, means for switching the power supply of the motor for a loaded state or non-loaded state in dependence upon the detected control variables.
 11. The hydraulic pump device as claimed in claim 10, wherein the control variable is the motor current and/or the pressure and/or the motor torque.
 12. The hydraulic pump device as claimed in claim 11, wherein the process of determining the drop in voltage at a resistor comprises means for detecting the motor current.
 13. The hydraulic pump device as claimed in claim 11, wherein a current measuring device comprises means for detecting the motor current.
 14. The hydraulic pump device as claimed in claim 10, further comprising a storage medium in which the second threshold value is continuously updated.
 15. The hydraulic pump device as claimed in claim 10, wherein the control variable is measured over a time interval.
 16. The hydraulic pump device as claimed in claim 10, wherein the load state switching of the hydraulic pump arrangement comprises a pulse width modulation of the motor voltage. 